Shear Lag in Shallow Wide-Flanged Box Girders

Abstract

The use of a reduced width of flange as a means of allowing for shear lag effects in wide shallow composite box girders with an overhanging top flange is examined. Equivalent widths with beam theory leads to a gross underestimation of the maximum stresses and deflections for girders with short spans and gives no significant improvement over the results obtained by beam theory alone for girders with long spans. Thus, equivalent widths do not provide an acceptable method of dealing with shear lag effects in wide-flange shallow box girders; simple beam theory without equivalent widths gives a satisfactory estimate of maximum longitudinal stresses and deflections for girders in which the span-to-width ratio is greater than 12 for the overhanging portion and greater than 5 for the central portion of a flange between two webs; and a more rigorous theory such as folded plate analysis should be used for girders in which the foregoing span-width ratios are not satisfied.